LACTONE-STRUCTURE OF SUGARS 75 



removes it from the solution; the oxide form is then no longer in 

 equilibrium and therefore regenerates the aldehyde form in the process 

 of regaining the equilibrium which has been disturbed. This fresh 

 supply of the aldehyde form in its turn reacts and is removed from the 

 solution, and so the process repeats itself until all of the sugar is used 

 up. At the same time this view of the structure of the sugar enables 

 us to understand why it is that although they give most of the aldehyde 

 reactions, yet they give them much less energetically than the typical 

 aldehydes. 



We may also ascribe to the same source the fact that the sugars do 

 not react in stoichiometrical proportions with metallic oxides; in the 

 proportions, that is, which would be expected if a molecule of sugar 

 reacted quantitatively with a molecule of metallic oxide. We cannot 

 predict, by merely writing down chemical equations, how much of any 

 metallic oxide under given circumstances will be reduced by a given 

 amount of sugar. Instead, for every concentration of sugar employed 

 and for every circumstance of the reaction, we have to estimate afresh, 

 and by direct measurement, the reducing power of the sugar. These 

 measurements are commonly expressed in tables which denote the 

 relationship of reduced cupric oxide (or other metallic oxide) to the 

 quantity of sugar present in the solution investigated. But such tables 

 are empirically established and are therefore reliable only if the cir- 

 cumstances of concentration, reaction, temperature and so forth are 

 exactly the same as those which prevailed in the estimations from 

 which the tables were computed. 



REFERENCES. 

 GENERAL: 



Armstrong: The Simple Carbohydrates and the Glucosides. London. 2d edition. 

 Levene and Jacobs: Ber. d. d. Chem. Ges., 1910, 43, p. 3141. 

 PENTOSES: 



Levene and Jacobs: Ber. d. d. Chem. Ges., 1908, 41, p. 2703; 1909, 42, pp. 1198, 



2102 and 3247; 1911, 44, p. 746. 

 Grund: Zeit. f. physiol. Chem., 1902, 35, p. 111. 

 Bendix and Ebstein: Zeit. allg. Physiol., 1902, 2, p. 1. 

 Clark, E. B.: Jour. Biol. Chem., 1917, 31, p. 605. 

 PENTOSURIA: 



Garrod, A. E.: Inborn Errors of Metabolism. Oxford University Press, 1909. 

 DECOMPOSITION OF SUGARS: 



Neuberg, A.: Oppenheimer's Handbuch der Biochemie, Erganzungsband, 1913, 



p. 569. 

 Levene and Meyer: Jour. Biol. Chem., 1912, 11, p. 361; 1912, 12, p. 265; 1913, 14, 



p. 149; 1913, 15, p. 65. 

 AMINO-SUGARS: 



Levene: Jour. Biol. Chem., 1917, 31, p. 609. 



